This invention relates to an improved electric motor power assist system and more particularly to an improved method and device for detecting the manually inputted drive force to the system.
A wide variety of types of systems have been proposed wherein a manual force is assisted by an electric motor. In many of these types of systems, the amount of electric motor assist provided is related to the degree of manual force applied, among other things. Therefore, the mechanisms that operate on this principal generally require some form of manual force measuring device.
This is normally done by providing some form of lost motion connection in the connection between the element to which the manual force is applied and the thing to be operated. The manual force application is measured by determining the amount of lost motion that occurs. Thus, the sensors that operate on this principal require the addition of the lost motion connection to the mechanical transmission for coupling at least the manual force applying device to the load which is driven. This makes it difficult to embody the electric power assist in conventional mechanisms merely through the use of an added electric motor or the assist.
It is, therefore, a principal object to this invention to provide an improved force sensor arrangement for an electrically assisted, manually operated device and more particularly to an improved sensor for sensing the manual force applied without necessitating a lost motion connection.
For example, in one type of device, there is employed a planetary transmission which produces relative movement in response to the lost motion and this planetary transmission then drives a force sensor. Obviously, this not only complicates the system and adds to its costs, but also makes it difficult to apply the system to conventional non-assisted mechanisms.
In another type of arrangement, the lost motion is measured by a pair of cylindrical cams which are held in contact with each other by a spring and relative movement occurs when the manual force is applied. The degree of manual force is measured by measuring the degree of relative movement. Again, this type of device adds to the costs and complexity of the system and makes it difficult to incorporate into conventional non-assisted mechanisms. In addition, the accuracy of these devices is dependent upon maintaining a consistent degree of lost motion for a given force input which requires bearings and lubrication and also which can be adversely effected by temperature changes.
It is, therefore, a still further object to this invention to provide an improved force sensor for an electric power assisted system wherein lost motion is not necessary in order to measure the applied force.
As noted above, temperature variations can result in variations in the amount of assist provided in response to a given input force. Even if lost motion is eliminated, this can still present some problems. It is, therefore, a further object of this invention to provide an electric power assisted system in which temperature variations will not adversely effect the performance.
The type of power assist mechanisms previously employed have not lent themselves to applications where such assist is desirable. For example in winding drums such as fishing reels power assist is desirable, but not possible with the power assist mechanisms previously employed. It is, therefore, a still further object of this invention/n to provide a compact power assist mechanism that is compact enough for such applications.
A first feature of this invention is adapted to be embodied in an electrically assisted, manually powered unit. The unit includes a manual drive element receiving a manual input force from an operator, an electric motor for providing an assist force, a transmission arrangement for receiving a driving force from the manual drive element and the electric motor and driving the unit. A force sensor senses the manual force applied to the manual drive element and delivers an output signal indicative of the manual force. A control controls the operation of the electric motor. The control has a sensor input stage receiving the signal from the force sensor and a logic for determining the operation of the electric motor from at least the signal from the force sensor. The force sensor provides the force signal without necessitating any significant displacement of a component thereof.
Another feature of the invention is adapted to be embodied in an electrically assisted, manually powered unit. The invention in accordance with this feature includes a manual drive element receiving a manual input force from an operator. An electric motor for providing an assist force is also used. A transmission arrangement receives a driving force from the manual drive element and the electric motor for driving said unit. A force sensor senses the manual force applied to the manual drive element and delivers an output signal indicative of the manual force. A control controls the operation of the electric motor. The control has a sensor input stage receiving the signal from the force sensor and a logic for determining the operation of the electric motor from at least the signal from the force sensor. The force sensor includes a first electrical device providing a signal indicative of applied force. A second electrical device capable of providing a signal indicative of applied force is also employed. The manual force is applied only to the first electrical device. The first and the second electrical devices are positioned in proximity to each other so as to experience the same temperature. Finally, a circuit connects the first and the second electrical devices to provide a temperature compensated signal to the sensor input stage of the control.
A third feature of the invention is adapted to be embodied in a an electrically assisted, manually powered reel. The reel includes a manual drive element receiving a manual input force from an operator, an electric motor for providing an assist force, a transmission arrangement for receiving a driving force from the manual drive element and the electric motor and driving the reel. A force sensor senses the manual force applied to the manual drive element and delivers an output signal indicative of the manual force. A control controls the operation of the electric motor. The control has a sensor input stage receiving the signal from the force sensor and a logic for determining the operation of the electric motor from at least the signal from the force sensor.